Hurricane season in the eastern Pacific begins today.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In the northeastern Pacific, they tend to form between May 15 and November 30. This early start is related to the basin’s warm sea surface temperatures and relatively low wind shear.

While powerful, these Pacific storms are generally not as familiar to Americans as those that form in the Atlantic. This is because they rarely make landfall in this country. In fact, it has only happened twice. A hurricane slammed San Diego, CA in 1858 and a tropical storm battered Long Beach, CA in 1939. This low rate of occurrence is attributed to the cold water of the California Current that flows south along the west coast. Nonetheless, Pacific hurricanes can still impact the US.

Developing in the tropics, Pacific storms deteriorate as they travel north to cooler waters and in some cases over the mountains of Mexico. However, their remnants are still laden with moisture when they reach the southwestern US, where they often unleash flooding rains.

East Pacific storms can also cross into the Central Pacific and affect Hawaii. (The dividing line between the two basins is 140°W longitude.) One such storm was Hurricane Iniki in 1992, the worst hurricane in the state’s history. With wind speeds measured up to 145mph, it was rated category-4 on the Saffir-Simpson scale.

This year, the eastern Pacific hurricane season got off to a record early start, with the development of Tropical Storm Adrian on May 9. No other storm in the basin has formed earlier during the satellite era.

Source: WMO